Liquid crystal displays are widely used for portable computer, television, various domestic electrical appliance displays, industrial display instruments, automobile meters, desktop monitors, aerospace field and so on due to the characteristics of low energy consumption, long service life, low affect to human bodies and environment, and convenient for carrying. The common working modes of liquid crystals comprise: TN (twist nematic), STN (supertwist nematic), TFT (thin film transistor), GH (guest-host) and so on.
Among others, TFT uses thin film transistor array to drive the liquid crystal molecules directly, which eliminates the cross distortion effect, thus the capacity for the displayed information is large. In combination with the use of liquid crystal material with low viscosity, the response speed of TFT is extremely increased and is able to satisfy the need by video image display, hereby the TFT display mode has currently become a mainstream display mode for high grade displays. The TFT display modes are in turn divided into IPS (in-plane switching), VA (vertical arrangement), TN (twist nematic phase) modes. Among others, the VA mode as well as the MVA and PVA modes developed therefrom all use liquid crystal materials with negative dielectric constants. The VA, MVA and PVA display modes driven by active matrices are relatively competitive for display with high response speed, wide viewing angle and high definition. Therefore, the chemosynthesis experts make their constant efforts to synthesize negative liquid crystals having new structures and good performances.
The liquid crystal materials used for VA display mode require low-voltage driving, high response speed and relatively wide operating temperature range, especially require stable properties in low temperature status, which demands the liquid crystal having characteristics of absolutely large dielectric constant, low viscosity, high clearing point, low melting point and so on. The product of birefringence (Δn) and cell thickness (d) relates to the wavelength of incident light (γ), thus it will not be appropriate to achieve high response speed by largely reducing the cell thickness. In general, the response speed is increased by decreasing viscosity; meanwhile, the response speed can also be increased by increasing the elastic constant of the liquid crystal materials.
As the displays set requirements on various indexes of the liquid crystals, a single compound is difficult to satisfy all the strict requirements in practical applications. The functional shortcomings can be complemented by scientifically compounding different liquid crystal monomers, so as to achieve the purpose of enhancing the display property, which requires the liquid crystal materials mixed together having good miscibility necessarily. Such liquid crystal is affected by the environment little, which will not result in either crystallization or occurrence of smectic phase at a lower temperature, so as to widen the applicability ranges of the liquid crystal.
Generally, the incorporation of separate unsaturated double bonds into the molecules of a liquid crystal can increase the elastic constant of the liquid crystal, increase the solubility property, result in excellent fluidity at low temperatures, increase the clearing point and decrease the crystallization temperature. The incorporation of soft groups in the molecules can decrease the possibility of formation of the smectic phase, and increase the solubility of the liquid crystal.
Patent 1, WO9827036A1, discloses a compound comprising butane as a bridge in the structure, whilst it never further concerns liquid crystals of butylenes. Patent 1 provides the properties and related data of the compound, but the range of the liquid crystals is not broad enough.
Patent 2, WO2008090780, relates to liquid crystals of butylenes in the structure, while it does not concern either the negative liquid crystals or the compounds of the present invention.
The present invention develops a series of new negative liquid crystals, having a relatively broad range for the phase transition of liquid crystal and good chemical stability. The addition of the new liquid crystals in mixed liquid crystals can reduce the solidifying point, increase the clearing point, and can increase the absolute value of the negative dielectric constant, so as to be much valuable in applications.